1. Field of the Invention
The present invention relates in general to new hardmask compositions having improved etch resistance for use in the manufacture of microelectronics devices. The compositions comprise metal-oxide precursors dispersed or dissolved in a solvent system.
2. Description of Related Art
The advances of microelectronic manufacture are reflected by the density and dimensions of semiconductor structures created by the microphotolithographic process. The demand for high density and small critical dimension (CD) has been constantly pushing photolithography technology to its limits. To keep pace with the semiconductor industry roadmap, next-generation patterning materials and innovative lithographic processes will be needed to work in unison for high-resolution lithography. As critical feature sizes keep shrinking to 32 nm and beyond, and while the aspect ratios of printed lines have certain limits to avoid possible line collapse, the use of a thin photoresist has been widely accepted to give better resolution and a large depth of focus (DOF). Rayleigh's law can be used to define the pattern resolution and depth of focus (DOF).Resolution=k1λ/NA; andDOF=k2λ/NA2,where λ is the irradiation wavelength, NA is the numerical aperture of the exposure tool, and k1 and k2 are constants for a given process. Rayleigh's theory indicates that an exposure tool with short wavelength and large numerical aperture will produce better pattern resolution. This principle is why the microelectronics industry has been progressively moving toward short exposure wavelengths. However, Rayleigh's law also shows that enhancing resolution causes the DOF to decrease. The use of a thin photoresist decreases the value of k1 and increases the value of k2, which results in better resolution and a large DOF. However, the reduced photoresist thickness cannot offer sufficient etch resistance to transfer the pattern into the substrate, especially for 193-nm ArF photolithography. Due to the transparency requirement, aromatic structures cannot be put into ArF resists, so most ArF resists etch even faster than previous photoresists. To solve this conflict between the need for ever-thinner photoresists for better resolution and the need for a sufficient etch budget for pattern transfer, only a few process and material solutions currently exist.
In one approach, silicon-containing hardmasks have been introduced into a multilayer etch stack to help provide a complete pattern transfer. Within a traditional trilayer process, the photoresist is coated on top of a film stack consisting of a thin silicon-containing layer on top of a thick carbon-rich layer. The alternating stack allows for selective etching between layers. A thick carbon-rich layer is typically used in order to provide the needed etch budget to create deep features in the substrate. The silicon hardmasks utilized within this scheme are usually applied using chemical vapor deposition or spin-casting. One of their drawbacks is the difficulty of obtaining sufficient lithographic performance for high-volume manufacturing. To circumvent this problem, silicon hardmask materials are often heated to high temperatures to facilitate densification of the film. A catalyst can also be added to the silicon hardmask formulation to lower the required baking temperature. Reactive ion etching (RIE) is typically used to open the hardmask layer under the photoresist. The hardmask-to-photoresist etch selectivity determines how thin the photoresist can be. Unfortunately, almost all currently-available photoresists still etch relatively rapidly under common hardmask plasma etch chemistries, and silicon hardmasks do not provide sufficient etch selectivity for thinner photoresists. Thus, the photoresist still must be substantially thick for high-resolution lithography.
Another solution is to use a developer-soluble underlayer material to eliminate the otherwise required etch step. Isotropically developable and photosensitive bottom anti-reflective coatings have been described. However, undercutting is very difficult to control in an isotropically developable bottom anti-reflective coating. For a photosensitive, anisotropically developable bottom anti-reflective coating, a major concern is bottom anti-reflective coating clearance and CD uniformity when it is coated on substrate topography. On the other hand, if they are coated on top of a spin-on carbon, planarization layer, those organic bottom anti-reflective coating materials are not effective as hardmasks.
More recently, multiple exposure technology for the next printing node has become the only viable option until exposure wavelengths shorter than 193 nm, such as 13.5 nm, are available. Many process schemes for multiple exposure technology have been investigated and reported. Some schemes utilized a bright field mask where only small portions of the photoresist, such as lines, are protected from the exposure, while the remaining portion of the resist is exposed. The photoresist is then contacted with developer to remove the exposed portions of the resist, thereby leaving only the unexposed portion of the photoresist (i.e., the lines) remaining above the hardmask layer. The pattern is transferred to the hardmask by etching away the hardmask layer except for those areas underneath the unexposed portions of the photoresist. The process is repeated until the desired pattern is achieved. In a dark field exposure process, a large portion of the photoresist is protected from exposure, while only the small portions of the photoresist are exposed and removed after development. As with bright field, the pattern must then be transferred to the hardmask using an etching process.
Thus, there is still a need in the art for improved hardmask materials that can provide much higher RIE selectivities compared to standard silicon oxide films, which would allow for thinner films and new process schemes that would not be possible with silicon alone. A hardmask with a sufficient etch selectivity could also eliminate the need for the spin-on carbon layer all together. There is also a need for hardmask materials which, in conjunction with spin-on-carbon layers, provide better reflectivity control than traditional anti-reflective coatings and potentially eliminate the need for such coatings in the multi-layer stack.